1. Field of the Invention
The invention is a method for recovering the data recorded on magnetic recording tape wherein adjacent layers of tape have become destructively adhered after long periods of storage on a spool.
2. Description of the Useful Arts
Magnetic recording tapes consist of magnetic oxide particles dispersed in a suitable polymeric binder material that is uniformly coated over the surface of a flexible film base material typically a polyester. The film base material is typically made of polyethylene teraphthalate (mylar) which is chemical and temperature stable and non-magnetic. The polymeric binder coating material is typically a polyurethane elastomer which contains a dispersion of gamma ferric oxide particles as well as numerous chemical constituents which give the recording tape its required particle dispersion, tape flexibility, conductivity, and relative softness which ensure intimate physical contact between the tape and the record/reproduce transducer.
The retention of the magnetically recorded data is performed solely by the gamma ferric oxide particles with the remaining constituents of the tape coating acting as a binder or carrier for these particles. Any distortion of the flexible film base or the coating or both, or any breakdown or alteration of the chemical structure of the binder will result in a mispositioning of the magnetic particles during operation, or a loss or misalignment of both the binder and particles. Such a loss or misalignment of the binder causes a loss of data on the magnetic recording tape. Studies have shown that other than from unwanted magnetic fields, there is almost no loss of data which does not stem from an alteration in some physical or chemical property of the polymeric binder material. Fortunately, many conditions which cause data losses through the physical and chemical deterioration of the binder can be controlled through temperature and humidity controls and regular tape rewinding.
Blocking is the term used in the art to describe the adhering quality or stickiness wherein magnetic recording tape, when wound up into a roll, cannot be unwound because it has adhered to itself. Blocking prevents the recovery of data from tape and resulting loss of data. Information is recorded in 9 tracks (channels) on 1/2-inch wide tape at the level of 1600 bits per inch. A small disruption in the continuity of the magnetic layer containing the densely packed data matrix due to tape adherence, causes a loss of the data on the tape.
In order to eliminate adhesion of magnetic recording tape it is recommended that stored tape be rewound on a semiannual or annual schedule. If the tape has been maintained in a temperature and humidity controlled environment, i.e. 17.degree. C. (62.degree. F.) to 20.degree. C. (68.degree. F.) and 35% to 45% relative humidity, the interval between rewinds can be extended to 3.5 years. (Care and Handling of Computer Magnetic Storage Media, NBS Special Publication 500-101, U.S. Dept. of Commerce, issued June 1983, pp. 82-83.) Applicant has found when rewinding of stored tape is omitted, that after about 4 years sporatic, unpredictable self adhesion of tapes occurs with the complete loss of data even though the tape is stored in the recommended, climate controlled environment.